TUOL SLENG , Cambodia -LRB- CNN -RRB- -- The trial of a former prison chief with the Khmer Rouge movement resumed inside a packed Cambodian courtroom Monday , with prosecutors painting a grim picture of inmates who were electrocuted , whipped and beaten to death .

Duch ran a prison where people were tortured and killed under the Khmer Rouge .

Kaing Guek Eav , a former math teacher and a born-again Christian , displayed no emotion as the U.N.-backed tribunal accused him not just of overseeing the torture and killing of more than 15,000 men , women and children three decades ago -- but of actively taking part in some of them .

The trial of the 66-year-old man , better known as Duch , resumed Monday just outside the Cambodian capital , Phnom Penh .

Spectators , many of them survivors of the abuse , watched the proceedings from an auditorium separated from the courtroom by a large glass window .

The proceedings began with Duch offering a basic introduction of himself . Court officials then read out the findings of their lengthy investigation .

Prosecutors contend Duch ran S-21 , a prison that had been converted from a school . Here , men , women and children were shackled to iron beds and tortured -- before they were beaten to death , prosecutors said .

Many of the victims were military officials or Communist Party members targeted for not going along with the philosophy of the ultra-Maoist Khmer Rouge movement , prosecutors said .

Duch faces charges that include crimes against humanity , war crimes , torture and murder .

He has admitted his role in the Khmer Rouge 's genocidal reign . Watch why his trial is significant ''

The movement swept to power in 1975 . Three years , eight months and 20 days later , at least 1.7 million people -- nearly one-quarter of Cambodia 's population -- were dead from execution , disease , starvation and overwork , according to the Documentation Center of Cambodia .

The non-profit organization has been at the forefront of recording the atrocities committed during the Khmer Rouge regime .

S-21 was one of 189 similar institutions across Cambodia . Duch is the first former Khmer Rouge leader to stand trial .

The tribunal , which is made up of Cambodian and international judges , does not have the power to impose the death penalty . If convicted , Duch faces from five years to life in prison .

The trial is expected to last three or four months .

`` Probably the most important thing about this court is : even after 35 years , you are still not going to get away with it . That is the message , '' said Chief Prosecutor Robert Petit .

Even though Duch was not a senior leader with the movement , many Cambodians were relieved that one of the regime 's former leaders was facing justice , said Youk Chhang , head of the Documentation Center of Cambodia .

`` I think there is a feeling of , well you know , finally -- now it 's finally happening after all these years of waiting -- hearing , fighting , negotiating , '' he told CNN last month . `` People have that kind of sense of relief that it 's now moving . When I ask people around the center today , people say , ` Oh , it 's about time . ' ''

Four of the regime 's former leaders , also accused of war crimes and crimes against humanity , await trial before the tribunal . The regime 's leader , Pol Pot , died in 1998 .

`` It all seems so fresh , '' said Norng Champhal , who was a starving little boy when Vietnamese forces invaded the prison . He was separated from his mother after a night in the prison and never saw her again .

`` It 's hard to control my feelings when I see this , '' he said , as he watched footage of the prison taken 30 years ago . `` I wonder whether my parents were tortured like these people , '' he said .

CNN 's Dan Rivers contributed to this report .

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NEW : Duch offers basic introduction of himself ; court officials read probe 's findings

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Duch 's trial is taking place outside the Cambodian capital , Phnom Penh

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Prison victims were military officials , Communist Party members

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Duch , former prison chief , has admitted role in Khmer Rouge 's reign